1. Field of the Invention
This invention relates to an image forming apparatus using an electrophotographic process, and more particularly, to an image forming apparatus for exposing an image carrying member by an LED (light emitting diode) array.
2. Description of the Related Art
Apparatuses for removing unnecessary electric charges on an image carrying member using LED's in conventional copiers are disclosed in U.S. Pat. No. 4,585,330, Japanese Patent Public Disclosure (Kokai) Nos. 58-117569 (1983), 61-67875 (1986), 61-177474 (1986), 61-177475 (1986), 61-177476 (1986), 62-40476 (1987), and the like. In all of these disclosures, LED's are arranged in a direction perpendicular to the direction of magnification variation of an image carrying member, and the images of the LED's are projected upon the image carrying member with unit magnification by a normal lens array, a lens array having a refractive index distribution, or a reflective optical system.
In any method, however, since LED's are disposed in close contact with the image carrying member and the images of the LED's are projected with unit magnification, there are the following three disadvantages. First, since the images are projected with unit magnification, a very long array of LED's is required. A complicated optical member, such as a lens array or the like, is therefore required and the entire apparatus becomes large. Second, since such a long array of LED's is required, several LED chips must be arranged individually divided to form the array. Accuracy in arrangement pitch is therefore inferior and it is very difficult to provide a uniform distribution of the amount of light of projected images in the direction of arrangement, which has a ripple (variations). Third, since the LED's are arranged in close contact with the image carrying member, a space is required in addition to electrophotographic process regions (e.g. an exposure region, a developing region, a transfer region, a cleaning region and a charging region) around the image carrying member. The image carrying member must therefore be large and, as a result, the apparatus becomes large. The conventional methods have the inconveniences as described above.